The invention relates to an insulating layer for a rocket propellant or for a rocket motor. More specifically, the invention relates to an insulating layer installed in a rocket propellant or motor of the front or face burner type.
Rocket propellants or rocket motors of the front burner type are used in ever increasing numbers in so-called ram jet rockets. The propellant or rocket motor comprises an insulation layer which insulates the inner wall surface of the combustion chamber from the solid fuel body on all sides except the facing side from which the burning jet stream is ejected. Such insulating layers must satisfy, among other requirements, three primary requirements. First, the insulating layer must thermally insulate the fuel or propellant body against any heating of the rocket or flying body that may result due to air friction. Such insulation is necessary in order to prevent impairing of the burn-up and thus of the pressure work range due to a temperature increase of the fuel or propellant body. The second purpose for the insulation is to protect the wall of the combustion chamber during the combustion of the fuel body against a too large heat-up. The third purpose of the insulation layer is not an insulating purpose, but rather a bonding purpose. The insulating layer shall be able to uniformly and rigidly bond the fuel or propellant body to the inner surface of the combustion chamber wall so as to prevent a separation of the fuel body from the combustion chamber wall. Such separation would result in hollow spaces into which the flame could flash-back in an undesirable manner.
German patent publication (DE-OS) No. 2,758 814 discloses an insulation layer for a rocket propellant which consists of an aziridin and a polybutadiene which includes hydroxyl end groups and which has been cured or hardened by means of a polyisocyanate hardener. This type of insulating layer is applied by covering the inner surface of the combustion chamber wall with the already hardened insulating layer. Thereafter, the propellant mass which has not yet been hardened is poured into the combustion chamber having the inner walls aligned with the already hardened insulating layer. Thereafter the so poured propellant mass is cured or hardened.
It is also known, that the insulating layer reduces the propellant or rocket motor diameter thereby also reducing the range of the respective rocket or flying body because the combustion chamber volume is usually predetermined, for example, by the size of the rocket and can therefore not be easily increased. Thus, it is desirable to achieve the above three purposes with an insulating layer which is as thin as possible, while still satisfying the mentioned requirements.